1. Field of the Invention
The present invention relates to a mobile communication system and a mobile communication method which control a transmission rate of user data to be transmitted from a mobile station to a radio base station via an uplink transmission rate allocation shared physical control channel, and transmit user data from the radio base station to the mobile station via a downlink shared physical data channel, and relates to a radio base station and a mobile station used in such a mobile communication system.
2. Description of the Related Art
By “3GPP” which is an international standardization organization for the third generation mobile communication system, high-speed radio-resource controlling methods used in the layer 1 and the MAC sublayer between a radio base station Node B and a mobile station UE have already been specified in order to effectively use the downlink radio resource. Such functions are collectively called the “HSDPA (High Speed Downlink Packet Access)”.
In HSDPA, the “HS-PDSCH (High Speed Physical Downlink Shared Channel)” is used as a physical data channel.
The HS-PDSCH is a shared channel. During a certain HS-PDSCH subframe, downlink user data is transmitted only to a certain mobile station.
Here, the length of an HS-PDSCH subframe is 2 ms (three slots). As shown in FIG. 1, the mobile station to which downlink user data is transmitted via the HS-PDSCH can be changed every 2 ms.
The AMC (Adaptive Modulation and Coding) is applied to the user data to be transmitted via the HS-PDSCH. The TBS (Transport Block Size) of such user data is adaptively changed in accordance with the downlink channel quality of the mobile station UE and the available transmission power resource of the radio base station Node B. Here, the TBS means the amount of the user data transmitted by an HS-PDSCH subframe.
Specifically, as shown in FIG. 1, the HSDPA is configured so that the better the downlink channel quality of the mobile station UE is, or the larger the available transmission power resource of the radio base station Node B is, the larger the TBS of the user data to be transmitted via the HS-PDSCH becomes, and the higher the transmission rate of the user data to be transmitted via the HS-PDSCH becomes.
In addition, in the HSDPA, the “HS-SCCH (High Speed Shared Control Channel)” is used as a physical control channel.
Control information, such as mobile station identifiers (UE-IDs) and TBSs, which is necessary for mobile stations UE to correctly receive the HS-PDSCH, is transmitted via the HS-SCCH.
While the length of an HS-SCCH subframe is 2 ms, which is equal to the length of an HS-PDSCH subframe, the HS-SCCH subframe is transmitted at the frame timing two slots earlier than that of the HS-PDSCH subframe.
Accordingly, as shown in FIG. 1, since the mobile station identifier is mapped to the first slot of the HS-SCCH subframe, the mobile station UE can avoid receiving the HS-PDSCH subframe assigned to another mobile station DE.
By shifting the transmission frame timing of the HS-SCCH and that of the HS-PDSCH from each other in this way, a mobile station UE has no longer need to receive the HS-PDSCH subframe assigned to another mobile station UE.
On the other hand, however, the shifting of the transmission frame timing of the HS-SCCH and that of the HS-PDSCH from each other has caused a problem that the transmission power resource of the radio base station Node B cannot be fully allocated to the HS-PDSCH.
With reference to FIG. 2, such a problem will be explained in detail.
First, the radio base station Node B determines the transmission power resource allocated to the HS channels (the HS-PDSCH and the HS-SCCH).
In such allocation of the transmission power resource, appropriate transmission power resource is allocated to non-HS channels (the channels other than the HS-PDSCH and the HS-SCCH) on the basis of the past activity of the non-HS channels.
In general, the transmission power resource allocated to the HS channels is renewed every 10 to 100 ms.
Second, the radio base station Node B determines the transmission power resource allocated to the HS-SCCH.
Since the required quality (the required BLER) and the transmission rate of the HS-SCCH are constant, the transmission power resource allocated to an HS-SCCH is uniquely determined by the downlink channel quality of the mobile station UE to which the HS-PDSCH subframe corresponding to this HS-SCCH subframe is allocated.
If the HS-PDSCH is allocated to a different mobile station UE for each subframe, the power allocated to the HS-SCCH is also different for each subframe.
Third, the radio base station Node B determines the transmission power resource allocated to the HS-PDSCH.
The transmission power resource allocated to the HS-PDSCH is determined by subtracting the transmission power resource allocated to the HS-SCCH from the transmission power resource allocated to the HS channels.
At this time, the HS-SCCH subframes to be taken into consideration are the HS-SCCH subframe requiring larger transmission power resource, among the HS-SCCH subframe corresponding to the relevant HS-PDSCH subframe and the HS-SCCH subframe corresponding to the next HS-PDSCH subframe.
This is because, since the transmission frame timing of the HS-SCCH is two slots earlier than the transmission frame timing of the HS-PDSCH, the transmission frame timing of a certain HS-PDSCH subframe overlaps the transmission frame timing of the HS-SCCH subframe corresponding to the certain HS-PDSCH subframe and the transmission frame timing of the HS-SCCH subframe corresponding to the next HS-PDSCH subframe.
In FIG. 2, shown is a flow of the allocation of transmission power resource in the radio base station Node B.
The radio base station Node B allocates the transmission power resource to the HS channels at T0.
The radio base station Node B then starts to transmit the HS-SCCH subframe #1 at T2. The radio base station Node B has to transmit the TBS of the HS-PDSCH subframe #1 by the use of the HS-SCCH subframe #1. In other words, it is necessary that the transmission power resource to be allocated to the HS-PDSCH subframe #1 has already been determined at T1.
In addition, in order to determine the transmission power resource to be allocated to the HS-PDSCH subframe #1, it is necessary that the transmission power resource to be allocated to the HS-SCCH subframe #2 has already been determined. In other words, it is necessary that which mobile station UE the HS-SCCH subframe #2 is assigned to has already been determined.
For example, the radio base station Node B is required to have already scheduled, by T1, which mobile station UE the HS-SCCH subframe #2 is allocated to.
Since the transmission power resource to be allocated to the HS-SCCH subframe #1 is higher than the transmission power resource to be allocated to the HS-SCCH subframe #2, the radio base station Node B sets the transmission power resource to be allocated to the HS-PDSCH subframe #1 equal to that obtained by subtracting the transmission power resource allocated to the HS-SCCH subframe #1 from the transmission power resource allocated to the HS channels at T0.
In this case, also as shown in FIG. 2, although, during the first slot of the HS-PDSCH subframe #1, the transmission power resource allocated to the HS-channels is used without wasting the resource, during the second and third slots of the HS-PDSCH subframe #1, the transmission power resource is not fully allocated to the HS-PDSCH channel because the transmission power resource allocated to the HS-SCCH subframe #2 is significantly less than the transmission power resource allocated to the HS-SCCH subframe #1.
As described above, with regard to the conventional HSDPA, there has been a problem that there is a possibility that the transmission power resource allocated to the HS channels cannot be fully used because the transmission frame timing of the HS-SCCH and that of the RS-PDSCH are not synchronized.
By “3GPP”, high-speed radio-resource controlling methods used in the layer 1 and the MAC sublayer between the radio base station Node B and the mobile station UE have been studied in order to effectively use the uplink radio resource. Such studies or functions are hereinafter collectively called the “EUL (Enhanced Uplink)”.
With reference to FIGS. 3 to 5, shown is a part of content determined as a result of the studies of the EUL in the “3GPP”.
With reference to FIG. 3, a description will be given of the operation that a mobile station US transmits user data to a radio base station Node B in the EUL.
In steps S1001 and S1002, the uplink user data to be transmitted to the radio base station Node B is mapped to the E-DCH (Enhanced Dedicated Channel).
Here, the E-DCH is a transport channel, and the “QoS (Quality of Service) control” for the user data in the wireless section is performed on a transport-channel basis. Specifically, the QoS of the uplink user data is set through the encoding process, the retransmission control process and the like applied to the transport channel.
The mobile station UE encodes the uplink user data mapped to the E-DCH in a step S1003, maps the encoded uplink user data to the E-DPDCH (Enhanced Dedicated Physical Data Channel) in a step S1004, and transmits the uplink user data, which has been mapped to the E-DPDCH, to the radio base station Node B.
Here, the E-DPDCH is a physical channel, and the transmission method in the wireless section is determined in accordance with the physical channel. Specifically, the modulation method, the spreading ratio, the orthogonalization code and the like are determined in accordance with the type of the physical channel.
Next, with reference to FIG. 4, a description will be given of the operation that the radio base station Node B controls the transmission power of the E-DCH (E-DPDCH) transmitted by the mobile station UE.
In steps S2001 and S2002, the radio base station Node B generates the AG (Absolute Grant) in consideration of the transmission buffer state and the transmission power state of the mobile station UE, and the interference power state in the radio base station Node B, and the like. Here, the AG is the information concerning the absolute transmission power used for transmitting the E-DCH (E-DPDCH), which is granted to the mobile station UE by the radio base station Node B.
The radio base station Node B encodes the AG in a step 2003, maps the AG to the E-AGCH (E-DCH Absolute Grant Channel) in a step S2004, and, in a step S2005, notifies the mobile station UE of the E-AGCH to which the AG has been mapped. Here, the E-AGCH is a physical channel.
In a step S2006, the mobile station UE transmits the E-DCH (E-DPDCH) in accordance with the received AG (=X). Specifically, the mobile station UE transmits the E-DCH (E-DPDCH) within the range not exceeding the absolute transmission power used for transmitting the E-DCH (E-DPDCH), which is granted by the radio base station Node B.
As described above, the E-AGCH is a physical control channel for notifying the mobile station UE of the AG generated by the radio base station Node B, and, at the same time, is a shared channel. In other words, the E-AGCH is an uplink transmission rate allocation shared physical control channel.
As shown in FIG. 5B, the AGs for the plurality of mobile stations UE#1 to UE#k, which communicate with the radio base station Node B via the EUL, are time-multiplexed into one E-AGCH.
Specifically, the AGs for the plurality of mobile stations UE#1 to UE#k are given mobile station identifiers, and are time-multiplexed on an E-AGCH subframe basis. Here, the E-AGCH subframe is operated in 2 ms or 10 ms.
Each of the mobile stations UE#1 to UE#k always receives the E-AGCH. Each of the mobile stations UE#1 to UE#k is configured to allow the E-DCH transmission to reflect the AG, only when the mobile station identifier given to the AG relating to the received E-AGCH matches its own mobile station identifier. On the other hand, each of the mobile stations UE#1 to UE#k is configured to discard the AG, if the identifiers do not match.
The transmission power which the radio base station Node B uses for the E-AGCH is determined by the downlink channel quality of the mobile station UE to which the AG is transmitted.
Specifically, if the downlink channel quality of the mobile station UE to which the AG is notified is bad, the transmission power for the E-AGCH is set high. On the other hand, if the downlink channel quality of the mobile station UE to which the AG is notified is good, the transmission power for the E-AGCH is set low. In other words, the transmission power which the radio base station Node B expends for the S-AGCH can significantly vary for each E-AGCH subframe.
However, in the study of the EUL, the transmission frame timing of the E-AGCH has not been specified yet.
On the assumption that the EUL is applied to the uplink, and the HSDPA is applied to the downlink, when the transmission frame timing of the E-AGCH is shifted from the transmission frame timing of the HS-PDSCH as in the case of the transmission frame timing of the HS-SCCH, the problem that the transmission power resource allocated to the HS channels is not fully utilized as shown in FIG. 2 will be further broaden.
As described above, since, in the conventional HSDPA, the transmission frame timing of the HS-SCCH and that of the HS-PDSCH are not synchronized, and, in the conventional EUL, the transmission frame timing of the E-AGCH is not clearly specified, it is conceivable that the transmission frame timing of the E-AGCH and that of the HS-PDSCH are also not synchronized, and there is a problem that there is a possibility that the effective use of the transmission power resource allocated to the HS channels is further inhibited.